Concern has grown in the airline industry about the potential for harm to nonsmoking airline passengers and crew members who are forced to breathe air contaminated with possibly carcinogenic byproducts of cigarette smoking. Accordingly, it has become increasingly important to develop an aircraft cabin ventilation system that exhausts air heavily contaminated with smoke and other exhalants to avoid circulating the contaminated air into the supply airstream where it may affect other passengers and the crew of the aircraft.
An aircraft cabin comprises a sealed, pressurized chamber. As air is vented overboard both intentionally and from small leaks at doors and at other points, fresh air is compressed, temperature conditioned and mixed with recirculated air as necessary for proper ventilation and maintenance of cabin pressure. In prior aircraft ventilation systems, air is drawn from various points within the cabin and recirculated as if the cabin comprised but a single uniformly contaminated zone. Because the source of smoke and most other exhalant contaminants in an aircraft cabin is the passengers who are seated in the cabin, and because the concentration of these contaminants is much greater at and above the heads of the passengers, viewing the aircraft cabin as a single zone is inaccurate. Since most passenger aircraft are provided with an overhead shelf or storage bin, the lower surface of this shelf tends to delineate the upper boundary of an upper zone that is most heavily contaminated with smoke and exhalants. Conversely, because the concentration of these contaminants in air adjacent the floor of the cabin is much less, the floor of the cabin space defines the lower boundary of a lower zone. In prior aircraft ventilation systems, air drawn from the more heavily contaminated upper zone is mixed with cleaner air drawn from the less contaminated lower zone, and a portion of the mixed air is vented overboard while the majority of the mixed contaminated air is recirculated back into the supply airstream. Thus, the prior ventilation systems succeed in contaminating all the air in the aircraft.